By design, detersive surfactants, generally present in excess in products such as shampoos, bodywashes, liquid soaps, laundry detergents, and toothpaste, are meant to remove dirt, oil, grease, and particulate matter from the hair, skin, fabric, and teeth. Nonetheless, it is desirable that one or more functional materials, called herein “benefit agent” or “active”, contained in these cleansing products, can be deposited and retained at relatively high levels on the substrates being cleaned, while maintaining detergency and foaming properties of these products. These actives, having benefits related to hair-care or skin-care or fabric-care or dental-care may range from silicones used as hair-conditioning agents, to emollient oils and fragrances used as skin-moisturizing and aesthetic/sensory property-boosting agents. Most of these benefit agents tend to be expensive, and hence can be included in the detersive products only at relatively low to moderate levels. Adequate deposition and retention of these actives, therefore, is critical to realizing their end-use benefits, when they are to be delivered through shampoos, soaps, laundry detergents, and toothpastes.
The prior art includes numerous patents describing methods for improving the deposition of hydrophobic or water-immiscible actives from detersive or wash-off product compositions, many of which involve the following:                i) the use of O/W emulsions of benefit agents, wherein a water-immiscible liquid (e.g., silicone), used as a benefit agent, is emulsified in water using an emulsifier selected from nonionic, anionic, and cationic surfactants;        ii) encapsulation of benefit agents within a polymeric capsule or shell, by curing or hardening a polymeric film as a capsule wall over droplets containing a benefit agent, or by encapsulating a benefit agent within a capsule wall comprising a complex coascervate of polymers, e.g., a complex coascervate comprising a polycation and a polyanion.        
A majority of these reported inventions, for example, the ones described in U.S. Pat. Nos. 3,723,325, 5,085,857, 5,500,152, 5,543,074, 5,776,443, 5,853,707, 5,990,059, 5,935,561, 5,923,203, 6,126,954, 6,156,713, 6,277,361 B1, 6,436,383 B2, 6,706,258 B1, U.S. patent application 2005/0158266, and WO 98/11869 rely on cationic polymers as a deposition-aid. Accordingly, these polymers are often referred to as deposition polymers in the art.
Despite the abundance of patents disclosing cationic polymer-aided methods for enhancing the deposition of hydrophobic benefit agents from surfactant-laden compositions, there is a need for substantially improving the deposition efficiency, given, for example, that most consumers who seek relatively high levels of hair-conditioning prefer conditioners, the non-detersive hair-conditioning products, to the detersive products like 2-in-1 shampoos which typically contain cationic polymers as a deposition-aid. A reason for this consumer preference is that, with the 2-in-1 shampoos, a substantial amount of the hair-conditioning agent, silicone, is rinsed away during shampooing, despite the deposition polymers contained therein.
In light of the distinguishing features of the present invention over the prior art, it appears that one plausible cause for the inadequate performance of the cationic deposition polymers as used in the prior art is that these polymers and the benefit agents are added as separate ingredients in producing the final detersive compositions, i.e., the deposition polymer(s) is not pre-adsorbed or pre-disposed to bind onto the benefit agent(s) as these ingredients are incorporated into the final compositions. As described herein, in order for the cationic polymer to function adequately as a deposition-aid, it must first physically attach onto the benefit agent. Given that most cleansing products contain relatively high amounts of anionic surfactants, and in contrast, relatively low levels of benefit agent(s) and a deposition polymer, binding of the deposition polymer onto the benefit agent may not be possible when these ingredients are added separately as ingredients to the detersive compositions, for reasons such as the following:                i) factors such as high concentration of anionic surfactants, and strong interaction (electrostatic) between an anionic surfactant and a cationic polymer are likely to favor association between the anionic surfactants and the cationic polymer over that between two weakly interacting, low-level ingredients, the cationic polymer and the hydrophobic benefit agent, especially considering that the commonly used cationic deposition polymers (for example, cationic cellulose and cationic guar derivatives) are mostly hydrophilic polymers that tend to have a low affinity for hydrophobic surfaces such as the surfaces of hydrophobic benefit agents;        ii) since the amount of an anionic surfactant likely to adsorb on the hydrophobic benefit agent would be much smaller than the amount of the surfactant remaining dissolved (i.e., non-adsorbed) in the solution-phase, the cationic deposition polymer is most likely to (associate) form complexes (anionic complexes in anionic surfactant-rich solutions) with the dissolved surfactant molecules rather than with any surfactant molecules pre-adsorbed on the benefit agent;        iii) being present at a much higher concentration than any cationic polymer-anionic surfactant complex that could possibly form, and having a diffusivity much higher than that of such a complex, the anionic surfactants might adsorb on the hydrophobic benefit agent far more easily than the polymer-surfactant complex, implying that the cationic deposition polymer may not be able to adsorb on the benefit agent to any considerable extent, when these two materials are added separately as ingredients to anionic surfactant-rich cleansing product compositions; and        iv) the hydrophobic benefit agent may simply dissolve in the surfactant-rich solution.        
In fact, it is often theorized in the art that association between the cationic deposition polymer and the hydrophobic benefit agent is achieved only when the cleansing products get heavily diluted during the course of the rinsing process. Clearly, large portions of the added deposition polymer and the benefit agent would be rinsed off before this optimum dilution level is reached.
Albeit, the prior art reveals approaches other than the use of cationic deposition polymers, for example, as disclosed in the U.S. Pat. Nos. 5,726,138, 6,541,565 B2, and 6,667,029 B2, the commercial detersive products continue to rely on these polymers for the deposition of hydrophobic benefit agents. This is likely because the deposition polymer-free approaches are not commercially viable from the standpoint of cost, product stability, and bulk manufacturing.
The prior art also includes methods wherein hydrophobic benefit agents are encapsulated within a capsule wall comprising a polymeric material. The encapsulated benefit agent is subsequently mixed into a cleansing/wash-off product composition comprising one or more surfactants. This final composition may further contain a cationic polymer, with the cationic polymer coating the capsule wall, as disclosed in U.S. Pat. No. 7,118,057 B2 and U.S. Pat. No. 7,294,612 B2.
The prior art also teaches that a cationic polymer may be an integral part of a capsule wall enclosing a benefit agent, with the capsule wall comprising a complex coascervate of a polycation and a polyanion, as revealed in WO 98/11870. According to a disclosure in WO 98/11870, the cleansing composition may further contain a cationic polymer-based thickening agent which remains dissolved in the aqueous solution phase of the composition. The encapsulated droplets have a particle size distribution such that at least 10% by weight of the droplets comprises relatively large particles having a diameter of at least 100 microns. As noted in WO 98/11870, the efficacy of the claimed compositions relies heavily on parameters such as the relative hardness/softness and the thickness of the complex coascervate capsule wall, as well as the size of the encapsulated droplets of hydrophobic benefit agents, which would be hard to control in a cost-effective manner, especially during bulk manufacturing. Furthermore, while it might be possible to use a thickening agent in certain cleansing products such as shampoo and bodywash, for minimizing gravity-separation of relatively large suspended droplets (particle size >>1 micron) from a product formulation, avoiding product instability in the way of gravity-separation of a key ingredient, might be impossible for liquid detergents which are generally required to have a relatively low viscosity and hence have a relatively low particulate-suspending ability. In addition to these specific concerns regarding the compositions in WO 98/11870, one skilled in the art would be particularly wary about a major limitation that applies, in general, to any encapsulation approach, as discussed below.
In order to adequately realize the end-use benefits, for example, hair-conditioning, fabric-softening, and fragrance-extension, of the hydrophobic benefit agents, while it is essential that there is substantial deposition of the benefit agents on the treated substrate, it is equally important that the benefit agents, once deposited on the substrate, are available in a physical form that is suitable for providing the desired end-use benefit. For example, deposition of a hydrophobic substance such as silicone on the hair or on a fabric causes hydrophobic-modification of the hair or the fabric surface, which in turn leads to effects that manifest as hair-conditioning or fabric-softening benefits. Nonetheless, if the silicone is encapsulated within a polymeric capsule, and should the encapsulated silicone droplet deposit on a substrate, it is the outer surface of the capsule wall and not the strongly hydrophobic surface of the silicone droplet, which would ultimately impart any effect in the way of modification of the substrate-surface. If the capsule wall is derived from hydrophilic, water-soluble polymers, as disclosed in U.S. Pat. Nos. 7,118,057 B2, 7,294,612, and WO 98/11870B2, the outer surface of the capsule wall may not be able to provide for hydrophobic-modification of the hair or the fabric surface, essential to delivering benefits such as hair-conditioning and fabric-softening.
In other words, even after substantial deposition of a benefit agent, it may not be possible to realize the end-use benefits, if the benefit agent is deposited in an encapsulated form comprising a shell of a capsule wall and an inner core of the benefit agent. In that case, at best, one can hope to see only a partial benefit of the benefit agent, relying on diffusion of the benefit agent through the capsule wall and/or leakage of the same due to any breakage of the capsule wall (for which hardness/softness and thickness of the capsule wall would be the efficacy determining factors, as revealed in WO 98/11870). Such subdued or partial availability of the benefit agent, despite its adequate deposition, may provide for a level of end-use benefit (e.g., fragrance emission) that may be sufficient, for example, for post-wash fragrance-extension, but too little for any appreciable hair-conditioning and fabric-softening.
It is therefore an object of the present invention to provide a more efficient method than the methods described in the prior art, for the deposition and retention of hydrophobic or oil-based benefit agents from detersive and/or rinse-off compositions. It is a further object that the compositions and methods described herein, do not involve encapsulation of benefit agents within any capsule wall, are relatively inexpensive, involve manufacturing steps that are easy to implement or control, and do not adversely affect the stability, detergency, and foaming properties of the cleansing product compositions. A related object is to provide stable, low-cost, compositions that allow significantly high deposition and retention of hydrophobic benefit agents onto substrates being treated with the compositions, including the fabric, hair, and skin.
Furthermore, it would be highly convenient to have hydrophobic benefit agents available in a form which can be incorporated easily into a final product composition. In that vein, it would be of much benefit, if such an additive-form for the benefit agent also served towards attaining an enhanced deposition of the benefit agent. Nonetheless, an important issue to be addressed in producing this additive-form is its long-term storage stability. It is therefore a further object of the compositions and methods to provide a highly stable additive-form for hydrophobic benefit agents, which, when incorporated into final product compositions, leads to an increased deposition of the benefit agents.
Several of the patents cited above, for example, U.S. Pat. No. 6,706,258 B1, describe the use of preformed oil-in-water (O/W) emulsions of hydrophobic benefit agents, wherein the oil-phase containing the benefit agent, is emulsified using (anionic, nonionic) surfactant-based emulsifiers. However, in the reported inventions, wherein a cationic polymer-based deposition-aid was used in conjunction with a preformed emulsion of a hydrophobic benefit agent (or with a hydrophobic benefit agent alone), the cationic polymer additive and the preformed emulsion (or a hydrophobic benefit agent alone) were incorporated into the final detersive composition as separately-added ingredients, i.e., no attempt was made therein to pre-adsorb or bind the cationic polymer additive onto the emulsion droplets (or the hydrophobic benefit agent) and subsequently mixing in the polymer-modified emulsion droplets (or the hydrophobic benefit agent) as a whole ingredient in producing the final detersive composition.
In fact, there is no known prior art document wherein a cationic particle and/or a cationic polymer-based additive was used as part of the emulsifier system used to produce a stable O/W emulsion of a hydrophobic benefit agent, that is subsequently incorporated into a surfactant-containing aqueous composition, with the composition exhibiting enhanced deposition of the hydrophobic benefit agent onto an intended site during use, along with good stability, and minimal detrimental effect on detergency and foaming properties, as in accordance with the compositions and methods described herein.